Many communications systems employ automatic repeat request (ARQ) techniques that allow a transmitter to confirm that data transmissions have been received successfully by an intended receiver. A typical ARQ technique involves the receiver responding to the transmitter with acknowledgment information for each received data block, with the acknowledgment information identifying the data block being acknowledged. The acknowledgment information may include a positive acknowledgment (referred to herein as an “ACK”) indicating that reception of the data block was successful, a negative acknowledgment (referred to herein as a “NACK”) indicating that reception of the data block was unsuccessful, as well as any other appropriate acknowledgment information. For example, in an enhanced general packet radio service (EGPRS) communication system, a receiver can acknowledge receipt of radio link control (RLC) data blocks using RLC/MAC control messages (where MAC refers to medium access control), such as an EGPRS packet downlink ACK/NACK (PDAN) control message or a packet uplink ACK/NACK control message.
In the case of a bidirectional communications system, such as an EGPRS system, the latency associated with using separate control messages to send acknowledgment information can be reduced (without significantly decreasing the bandwidth available for data transmission) by including such acknowledgment information with data blocks to be transmitted in the opposite direction. For example, EGPRS supports such latency reduction through its fast ACK/NACK reporting (FANR) procedure. The FANR procedure allows acknowledgment information to be piggy-backed with an RLC/MAC data block subsequently sent from a receiving unit to a transmitting unit through use of a piggy-backed ACK/NACK (PAN) field. EGPRS mobile stations can support two types of FANR procedures, namely, polled FANR and event-based FANR. Additionally, EGPRS mobile stations are able to respond to polls requesting acknowledgment information to be sent using PDAN control messages instead of PAN fields. In some scenarios, a conventional EGPRS mobile station will send duplicate acknowledgment information generated by these different acknowledgment procedures.